Alfalfa (Medicago sativa subsp. sativa) is the most important forage legume in the United States. Alfalfa is tetraploid, having 4 homoeologous chromosomes for each of the 8 different chromosomes, for a total of 32 chromosomes. It is highly desirable for hay production and pasture for livestock because it produces more protein per hectare than grain or oilseed crops, and requires little or no nitrogen fertilizer because of its ability to carry out symbiotic nitrogen fixation. However, alfalfa is very sensitive to aluminum toxicity.
Aluminum toxicity causes similar symptoms in many plant species. Micromolar concentrations of Al+3 can damage the root system, sometimes within minutes of exposure. Damage to the root system then significantly reduces yields due to an insufficient intake of water and other nutrients (Kochian, 1995; Kochian et al., 2004). Heavy applications of limestone and P fertilizer are commonly used to prevent yield loss, but these amendments are often not economical or practical.